The present invention is related to polyalkylsiloxane copolymers. More particularly, the present invention is directed to personal care compositions containing polyalkylsiloxane copolymer fluids or soft waxes as hair or skin treating agents.
Alkylpolysiloxanes are known in the art. Reference is made, for example, to U.S. Pat. Nos. 4,574,082 to Tietjen et al. and 3,418,353 (Brown).
In the patent to Tietjen et al., the internal silicon atoms are each bonded to a first alkyl group having 1-30 carbon atoms and a second alkyl group having 2 to 30 carbon atoms. The alkyl groups may be linear or branched. The alkylpolysiloxanes in Tietjen et al. are used in cosmetic products.
In the patent to Brown, the internal silicon atoms of the siloxane backbone are each bonded to a first organic group (designated as "R") which is methyl or phenyl and to a second organic group (designated as "R .sup.1 ") which is a monovalent hydrocarbon radical having at least two carbon atoms and being free of aliphatic unsaturation, at least 50% of the hydrocarbon radicals in the second organic group being alkyl radicals containing at least 12 carbon atoms. In Brown, it is said to be particularly useful if the second organic group, R.sup.1, is two different organic groups, i.e., R.sup.11 and R.sup.111, wherein R.sup.11 is an alkyl radical containing at least 12 carbon atoms and R.sup.111 is different from R.sup.11 and represents a monovalent hydrocarbon radical free of aliphatic unsaturation and containing at least two carbon atoms. The alkylpolysiloxanes in Brown are used as release agents in molding applications.
Conventional alkylpolysiloxanes containing linear alkyl side chains of a specific length or linear alkyl side chains which are all either higher alkyl or lower alkyl become hard and brittle as the alkyl side chain becomes longer. Their hard and brittle nature makes these conventional alkylpolysiloxanes unsuitable for use in hair and skin care compositions, which require more fluid or gel-like polysiloxanes in order to have effective application and payout onto the hair or skin surface.
The present invention is based on the discovery that polyalkylsiloxane copolymers containing mixtures of linear lower alkyl side chains and linear higher alkyl side chains or mixtures of linear alkyl side chains and branched alkyl side chains will have a broader melting transition, as measured by a differential scanning calorimeter, and will display a lower onset point and a lower peak, which indicates melt point depression due to structural variations. Thus, the polyalkylsiloxane copolymers used in this invention will be fluids or soft waxes at body temperature and will have improved application and payout (i.e., spreadability) on hair and skin. Surprisingly, it has also been found that the polyalkylsiloxane copolymers used in this invention have better substantivity and hair conditioning properties than the conventional alkylpolysiloxanes described above.